This invention relates to a method of effectively removing solids that have sedimented and remain in a rotary drum, of an industrial horizontal drum-type centrifugal separator which separates a slurry of either a singular solution or a mixture of composite solutions containing low concentrations of settleable substances into solids and liquid or into solids and liquids of different specific gravities (e.g., oil and water). This invention relates especially to the removal of a layer of solids that has stuck fast to the inner wall of the drum.
Drum-type centrifugal separators have extensively been used because their use of centrifugal force permits separation of mixtures that can be difficult to separate using other centrifugal separators, such as decanter type separators or disk-type centrifugal separators, and also because of the lower price of drum-type centrifugal separators as compared to the other types. When sediment has built up on the inner wall of the rotary drum of a centrifugal separator as a result of the separating operation is to be removed, it is standard practice to disassemble the machine and scrape off the sediment by hand or using manual scraping tools. This maintenance is essential for this type of centrifugal separator since the sediment not removed from the rotary drum will increasingly affect the clarity of the separated liquid.
Thus the use of larger centrifugal separators for greater treatment capacity has not been done because the attendant disassembly time required for the sediment removal from the rotary drum, and the corresponding decrease in operation time is even greater with a larger capacity machine. Given current practices, drum-type centrifugal separators are limited to use in situations where only small volumes of mixtures or mixtures with low solids content are treated for purification. In applications where larger quantities of mixtures or mixtures with high solids content are handled, either centrifugal separators of other types are used or a centrifugal separator of other type is combined with a drum-type centrifugal separator to perform two-step treatment.
The removal of solid matter that has deposited on the inner wall of a rotary drum, after disassembly, requires considerable time and labor, especially when the time span between stopping the machine and the disassembly is substantial, when a thick sediment has built up, or when the separated solids, by nature, harden readily.
As stated above, it has been standard practice with conventional drum-type centrifugal separators that, removal of sediment that has settled on the inner wall of the rotary drum has involved inefficient methods that consist, for example, of disassembling the machine and scraping off the sediment by hand or using manual scraping tools. Employment of larger machines to achieve greater treatment capacity has been hindered by the difficulties involved in the removal of sediment from the rotary drum as described above. Drum-type centrifugal separators have, therefore, been limited in use to the applications where only small volumes of mixtures or mixtures with low solids content are treated for purification. In applications where larger quantities of mixtures or mixtures with high solids content, other methods have to be employed, including combined use of the centrifugal separator with one of other separator types.
Thus it is the object of the present invention to obviate the above-described necessity of disassembling and the concomitant labor involved in the removal of sediment from the rotary drum and to automate the separation process.
It is another object of the present invention to permit the use of larger drum-type centrifugal separators than heretofore used without attendant increases in downtime for disassembly.
Still another object of the present invention is to preclude the necessity of disassembly and to automate the removal of sediment from drum-type centrifugal separators of the sizes currently in common use.
The present invention solves the foregoing problems by a cleaning method for removing sediment from the inner wall of the rotary drum of a horizontal drum-type centrifugal separator having first and second ends terminating in trunnions supported by bearings, the method comprising: charging a plurality of solid cleaning medium pieces into the rotary drum, supplying a cleaning liquid to the rotary drum, rotating the rotary drum, and to remove sediment from the inner wall thereof, discharging the sediment together with the cleaning liquid.
The solid cleaning medium may be charged into the rotary drum either before centrifugal separation or after the centrifugal separation, at the time the drum is cleaned, and may be added either together with the cleaning liquid or before the introduction of the cleaning liquid.
These two alternative procedures are defined as follows. The first procedure (hereinafter called Procedure 1) is a cleaning procedure for removing sediment from the inner wall of the rotary drum of a horizontal drum-type centrifugal separator having first and second ends terminating in trunnions supported by bearings, the method comprising charging a plurality of solid cleaning medium pieces into the rotary drum, allowing the solid cleaning medium pieces to deposit on the inner surface of the rotary drum, feeding a liquid to be treated, subjecting the liquid to centrifugal separation in batch operation to form a sediment, supplying a cleaning liquid to the rotary drum, rotating the rotary drum at a speed to attain not more than 1 G, to remove sediment from the inner wall thereof, and discharging the sediment together with the cleaning liquid.
The second procedure (hereinafter called Procedure 2) is a cleaning procedure for removing sediment from the inner wall of the rotary drum of a horizontal drum-type centrifugal separator having first and second ends terminating in trunnions supported by bearings, the method comprising: supplying a plurality of solid cleaning medium pieces and a cleaning liquid to the rotary drum while the drum is decelerating or after it has stopped, rotating the rotary drum at a speed to attain not more than 1 G to remove sediment from the inner wall thereof and discharging the sediment together with the solid cleaning medium pieces and the cleaning liquid.
In conformity with the invention, there is provided a horizontal drum-type centrifugal separator that does not require the conventional manual scraping off of sediment can be realized.